1. Field of the Technology
The present invention relates to communication techniques, and more particularly, to a method for improving the subscriber access capacity of a broadband access device.
2. Background of the Invention
A Virtual Local Area Network (VLAN) is used to divide a physical network section of a Local Area Network (LAN) into multiple virtual LAN network sections. The VLAN makes it possible to divide work groups based not only on physical locations but also on functions, applications or protocols as well, which improves flexibility and convenience of networking.
For the convenience of application, implementation of the VLAN in an Ethernet is regulated in 802.1Q (Virtual Bridged Local Area Networks) which is issued by Institute of Electrical and Electronics Engineers (IEEE). According to the regulations of 802.1Q, a 4-byte 802.1Q tag is added to a standard ethernet frame following source MAC address. FIG. 1 is a diagram illustrating a standard 802.1Q frame format, where—                Destination Address is a MAC address with 4 bytes,        Source Address is a MAC address with 4 bytes,        802.1Q tag is a 802.1Q tag field with 4 bytes,        Length/type is the length of data or the type of the ethernet frame with 2 bytes,        DATA is the data field carried by the Ethernet,        and Frame Check Sum (FCS) is a checksum of the ethernet frame.        
The 802.1Q tag added to the ethernet frame specifically includes: a 2-byte Tag Protocol Identifier (TPID) and a 2-byte Tag Control Information (TCI). The TPID, a new type defined by the IEEE and of which the value is a hexadecimal value of 8100, is used to identify the ethernet frame as an ethernet frame with an 802.1Q tag.
The detailed architecture of the TPID in the 802.1Q tag is shown in FIG. 2, where a Virtual Local Area Network Identifier (VID/VLAN ID) which is a 12-bit field used to identify different VLANs, and the value of the VID/VLAN ID ranges from 0 to 4095 so as to make 4096 VLANs be differentiated by different values. Each data frame sent by a device supporting 802.1Q protocol includes the TPID field to identify the VLAN to which it belongs.
Based on the above-mentioned regulations, in current broadband access networks, the broadband access device maps the location information of an accessing subscriber to the VLAN information of the 802.1Q and transmits, through the 802.1Q tag field carried by the data frame, the VLAN information of the 802.1Q acquired by mapping to a Broadband Remote Access Server (BRAS) device. The location information of the accessing subscriber can be an access port a Permanent virtual circuit (PVC), etc. When a subscriber authentication is completed, the BRAS is able to locate the subscriber according to the identifier (e.g. the hostname) of the BRAS itself, the slot number and the port number via which the broadband access device is connected to the BRAS, and the VLAN ID in the data frame of the subscriber.
However, as the VLAN ID field of the 802.1Q tag header has only 12 bits, 4096 VLANs can be identified at most. In a network in which a broadband access device and a BRAS device are networked directly, a continual enlargement of the scale of a single-node broadband access device enables the device to support more than 4096 subscriber access points. Moreover, a method adopting a cascading access solution to save fibers can result in high capacities access points with more than 4096 subscriber access capability. In such a case, 4096 VLANs are not enough to identify different subscribers.
In addition, since device manufactures and chip manufactures in the Industry have different focus on the 802.1Q, there are differences in supporting the 802.1Q standard. For example, although some lanswitch chipsets have unique features in providing some services, they do not support the identification of all the 4096 VLAN IDs, for instance, some chipsets only support the identification of 256 VLAN IDs. In such a case, the number of the subscriber access points which can be identified is much less.